Field of the Invention
The present invention relates to a method of reconnecting a radiocommunication terminal to a network. The method can increase the autonomy of the terminal (the time before the battery must be recharged) and reduce its wake-up time when a signal is again available. The present invention also relates to the corresponding terminal.
Description of the Prior Art
Radiocommunication terminals such as GSM or DECT cellular telephones, for example, must be within an area covered by a base station transmitting a signal in order to receive and send voice or other data.
Each transmitter delimits a geographical area referred to as a cell within which data reception is satisfactory. The density with which the cells, and therefore the transmitter stations, are distributed depends on their geographical location.
An urban area or a busy road has a relatively dense coverage, except in confined spaces such as car parks or indoor spaces (cinemas, theatres, etc), where reception is virtually impossible.
A mountainous or sparsely populated region has fewer stations, which are therefore further apart, and is less well covered.
To assure the user optimum signal reception regardless of their geographical location, the terminal scans the available frequencies continuously, using processes known in the art.
The quality of the received signal varies as the user moves around.
The signal becomes progressively weaker on moving away from the transmitter station of the cell in which the terminal is located. The terminal scans the various frequencies in the GSM band until it detects a signal of better quality than the signal it is currently using to communicate.
Once the new signal has been detected, the terminal uses means known in the art to connect to the new station, i.e. to change cell by selecting a cell adjacent the preceding one.
If no network is available, the terminal goes to a standby mode and scans the frequencies in a relatively wide frequency band, or even several bands in the case of a multiband terminal, at varying intervals, until a new cell can be selected.
In one prior art method the standby time of the terminal between two consecutive searches is increased, for example up to a maximum, and the search for a network then continues at regular intervals and covers all the frequencies.
The search for a terminal activates a large number of components in the terminal, leading to high power consumption and reducing the autonomy of the terminal.
The wake-up time, i.e. the time the terminal takes to change from a standby state to a signal receiving state as soon as an available network is detected, is long because all of the frequencies that the network can use are searched for a signal.
If the user enters a place where the network is not available, such as a car park or a tunnel, signal reception is suddenly interrupted and the terminal cannot access the network.
With prior art network detection methods, the terminal periodically searches all the frequencies of an available network even though it has just stopped using a particular frequency providing a high reception level.
This search consumes additional energy unnecessarily.
Quite apart from their excessive energy consumption, the prior art methods lead to long standby periods and relatively long wake-up times, during which the user cannot receive calls.
The long wake-up times also constitute a drawback for the network operators, who cannot offer services during these periods.
This being the case, an object of the invention is to alleviate the above drawbacks by proposing a method which reduces the power consumption of a radiocommunication terminal when no network is available and reduces its wake-up time as soon as a network is available again.